RU2229707C1 - Method of magnetic inspection of pipe-lines - Google Patents

Abstract

FIELD: nondestructive testing of pipe-line transport. SUBSTANCE: magnetic transducers positioned on magnetic neutral in interpolar space of permanent magnets are arranged at specified distance one from another so that plane of each transducer is parallel to lines of force of magnetic poles. Transducers are connected in pairs in compliance with differentiating circuit. Lateral and longitudinally oriented flaws in pipe are distinguished by characteristic indications of signals picked off transducers while magnetic system is moved inside pipe. EFFECT: enhanced reliability and sensitivity to detection of flaws in pipes of main lines. 5 dwg

Description

The invention relates to the field of magnetic non-destructive testing methods and can be used to detect defects in extended objects, for example, in pipes of a main pipeline transport.

There is a known method of magnetic control developed by RTC "Orgazdefectoscopy" and used in inspection shells "Krot-1000M" and "Krot-1200M" (see. "Additional materials"). In these flaw detectors, the method of recording the scattering of the magnetic flux arising above the defect is used. Signals from defects in the pipeline detected by the flaw detector shell are recorded and processed using computer programs and graphically displayed on the screen.

The disadvantage of this method is that when analyzing the information received, only the amplitude value of the signal is considered, which does not allow to reliably determine the type of defect.

A known method of magnetic control of pipelines (anniversary collection of MNPO "Spectrum", 1994, G.A. Zhukova, L.A. Khvatov, Development of a method and means of magnetic diagnostics of gas pipelines; see "Additional materials"), which consists in that sensors mounted around the circumference on the inside of the pipe detect a change in the magnetic field in the defect area. In this case, only the absolute value of the signal amplitude is analyzed, which does not allow to reliably recognize the type of defect and, in addition, makes it difficult to analyze due to registration by the signal sensors of interference associated with a change in the gap between the magnetic system and the inner surface of the pipe, a change in the speed of the magnetic system vibration, etc.

The closest in technical essence to the proposed method is a magnetic control method (Patent for the invention No. 2118816), which consists in the following.

The magnetic field sensors are installed in the magnetic system along one line perpendicular to the magnetic neutral, forming a "comb". At each measurement point, 2 sensors are installed to measure the tangential and normal field components.

A magnetic system with sensors moves over the tested surface of the product along the crack. When the magnetic system passes over the crack, the signals that are marked, i.e. carry information about the numbers and coordinates of the sensors from which they are taken.

The signals from the sensors compute the field strength vectors along the sensor installation line. According to the calculation of the field vectors, a vector field distribution function is constructed, which is compared with the vector distribution function introduced earlier in the computer memory. The comparison is carried out taking into account the presence of characteristic features. Then, using the formula dependencies entered into the computer memory and the measured values of the parameters, the characteristics of the cracks (depth, width, etc.) are calculated. The vector field distribution functions for identical cracks having different coordinates relative to the poles of the magnetizing device are different, since the background field is significantly different for these points.

In this method, the absolute value of the signal is taken from the magnetic field sensors, which makes it difficult to recognize longitudinal and transverse defects, since such signals are similar to interference signals that occur, for example, due to a change in the gap between the moving magnetic system and the inner surface of the pipe, oscillations of the magnetic system, changes in its speed, etc.

The proposed method is devoid of this drawback. In order to reliably identify transverse and longitudinally oriented defects in the pipe, a magnetic control method is proposed, the essence of which is as follows.

In the drawings indicated:

Figure 1 - arrangement of the magnetic system in the pipe:

a) the arrangement of the matrix of magnetic field sensors in the interpolar space;

b) a differential connection scheme for sensors in the “two through” version.

1 ... 10 - magnetic field sensors;

11 - longitudinal crack;

12 - transverse crack;

13 - direction of the generatrix of the pipe.

14, 15 - magnetic poles;

16 is a matrix of sensors.

Figure 2 - field distribution in the region of cuts in the region of templates, cut from the pipe:

a) distribution of magnetic field lines.

1 is a section of a pipe template;

2, 3 - accumulation of powder;

5 - an incision with a depth of 0.4 T;

6 - an incision with a depth of 0.15 T;

T is the thickness of the template (pipe);

t is the thickness of the non-magnetic layer;

L1 is the width of the region of accumulation of powder over an incision with a depth of 0.4 T;

L2 is the width of the region of accumulation of powder above the notch with a depth of 0.15 T;

7 - non-magnetic plate with a thickness of 5 mm;

N, S - poles of an electromagnet;

b) the indicator pattern of the powder settled in the area of the defect

Figure 3 - signal from a longitudinal crack.

4 is a signal from a transverse crack.

5 is a signal from interference (changing the gap between the magnetic system and the surface of the pipe) in a defect-free place.

The magnetic field sensors located on the magnetic neutral are placed at a distance of 5 ... 10 mm from each other, so that the plane of each sensor is parallel to the magnetic lines of force, and include pairwise according to the differential circuit. Depending on the requirements for the parameters of detected defects, the differential pair may include sensors located at a distance of 20 ... 30 mm from each other, and some sensors may be included in two differential pairs. An example of a differential connection circuit "in two" is shown in Fig. 1b (1-4, 2-5, 3-6, 4-7, 5-8, 6-9, 7-10 - sensors included in the differential circuit). By the type ("image") of the signals taken from the magnetic field sensors, a set of informative parameters is determined that allows one to distinguish between transverse and longitudinally oriented defects.

The differential connection of the magnetic field sensors can significantly compensate for the interference signal associated with a change in the gap between the magnetizing system and the inner surface of the pipe or other inspected object, as well as fluctuations and changes in its speed.

With the indicated method for connecting sensors, signals from longitudinal cracks have a characteristic sign that, depending on the location of the crack in the space between the sensors, the signals from one or more differential pairs of sensors will necessarily be in antiphase with respect to the signals from the remaining pairs of sensors of this magnetic system. In most cases, there is a certain phase shift between the signals from various sensors, since the direction of the crack, as a rule, is not strictly parallel to the direction of movement of the magnetic system, and the sensor location line is at an angle of 45 ° to this direction, and the sensors fix the defect in turn .

Signs that distinguish the signals from the transverse crack are a very sharp change in the amplitude of the signal, followed by a change in its polarity, a small signal duration and almost the same deviation of the amplitude both in the positive and negative regions. In addition, there is an almost constant phase shift between the signals from various differential pairs of sensors of the magnetic system (since the sensors fix the defect in turn).

And finally, the signal from the interference is different in that all the sensors react to the interference at the same time, so the signals from the sensors will change synchronously.

The proposed method is tested on an experimental stand.

During the experiment, the magnetic field sensors were located in the interpolar space along the magnetic neutral, and the magnetic system that moved along the pipe was installed so that the magnetic induction vector is directed at an angle of 45 degrees with respect to the pipe generatrix (Fig. 1a).

To select the optimal distance between adjacent sensors, the extent of the magnetic field over the inner surface of the pipe at a distance of 5 mm was experimentally determined. For this purpose, templates 1 were cut out of the pipe (Fig. 2), on the surface of which cuts 5, 6 of various depths were made. When placing template 1 in an electromagnet N, S and creating a magnetic field, an air suspension of a finely dispersed magnetic powder was deposited, which was deposited in the region of an artificial defect. Measurements of the width of the strip of settled powder, which is proportional to the effective value of the magnetic field over the defect, showed that when the depth of the crack changes within 15 ... 40% of the pipe wall thickness, the field length varies within 13 ... 16 mm. It was experimentally established that the distance between the sensors 5 ... 10 mm with a crack depth of at least 15% of the pipe thickness guarantees the appearance of a signal from the defect at least on one of the adjacent sensors. In addition, it was determined that the optimal distance between the sensors in the differential pair is in the range of 20 ... 30 mm. At a shorter distance, the level of the recorded signal decreases, since the field gradient at the points of location of the differential-connected sensors decreases. At a greater distance, the influence of the signal from interference increases, since, for example, due to local deformation of the pipe wall, the gap at the points where the sensors are located between the magnetic system and the inner surface of the pipe can noticeably differ.

Some of the results obtained are shown in Figs. 3, 4, 5. The indicated figures show the types of signals taken from magnetic field sensors from defects such as longitudinal and transverse cracks in the pipe wall, as well as signals associated with a change in the gap between the magnetic system and the inner surface of the pipe.

As can be seen from the data, the signals from the magnetic fields of multidirectional defects are fundamentally different from each other and from interference signals, which makes them easy to recognize.

Figure 3 shows the signal captured by five differential pairs of sensors during the passage of the magnetic system over a longitudinal crack in a pipe with a diameter of 1220 mm. A distinctive feature of a longitudinal crack in this case is that the signals from two differential pairs of sensors are out of phase with the other three pairs. In addition, there is some phase shift between the signals from the sensors.

Figure 4 illustrates the features characteristic of signals from a transverse crack. As indicated above, such signs are a sharp increase and decrease in the signal amplitude and a slightly different deviation of the signal amplitude in the positive and negative region. There is also a constant phase shift between the signals from various sensors of the magnetic system.

The signals from the sensors obtained when the magnetic system moves along the defect-free place of the pipe when the gap between the magnetic system and the inner surface of the pipe changes, are shown in FIG. In this case, all the signals from the sensors change in phase, which fundamentally distinguishes them from the signals received when passing over a longitudinal crack.

Thus, the above and justified set of features of the proposed method is necessary and sufficient to identify and recognize longitudinal and transverse defects in the pipes of the main pipeline.

Using the proposed method on flaw shells will provide reliable identification of longitudinal and transverse defects in the pipes of pipeline transport.

Claims (1)

The method of magnetic control in the in-pipe diagnostics, namely, that the magnetic field sensors are located in the pole space along the magnetic neutral, and the magnetic system is set so that the magnetic induction vector is directed at an angle of 45 ° relative to the generatrix of the pipe and move it along the pipe, different the fact that the magnetic field sensors are placed at a distance of 5-10 mm from each other, so that the plane of each sensor is parallel to the power lines of the magnetic poles, and include pairwise differential the circuit, and the distance between the differentially included sensors in each pair is set within 20-30 mm, and according to the characteristic features of the signal, transverse and longitudinally oriented defects in the pipe are distinguished.

Images